1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.pool2;
18
19 /**
20 * An interface defining life-cycle methods for instances to be served by an
21 * {@link ObjectPool}.
22 * <p>
23 * By contract, when an {@link ObjectPool} delegates to a
24 * {@link PooledObjectFactory},
25 * </p>
26 * <ol>
27 * <li>
28 * {@link #makeObject} is called whenever a new instance is needed.
29 * </li>
30 * <li>
31 * {@link #activateObject} is invoked on every instance that has been
32 * {@link #passivateObject passivated} before it is
33 * {@link ObjectPool#borrowObject borrowed} from the pool.
34 * </li>
35 * <li>
36 * {@link #validateObject} may be invoked on {@link #activateObject activated}
37 * instances to make sure they can be {@link ObjectPool#borrowObject borrowed}
38 * from the pool. {@link #validateObject} may also be used to
39 * test an instance being {@link ObjectPool#returnObject returned} to the pool
40 * before it is {@link #passivateObject passivated}. It will only be invoked
41 * on an activated instance.
42 * </li>
43 * <li>
44 * {@link #passivateObject} is invoked on every instance when it is returned
45 * to the pool.
46 * </li>
47 * <li>
48 * {@link #destroyObject} is invoked on every instance when it is being
49 * "dropped" from the pool (whether due to the response from
50 * {@link #validateObject}, or for reasons specific to the pool
51 * implementation.) There is no guarantee that the instance being destroyed
52 * will be considered active, passive or in a generally consistent state.
53 * </li>
54 * </ol>
55 * {@link PooledObjectFactory} must be thread-safe. The only promise
56 * an {@link ObjectPool} makes is that the same instance of an object will not
57 * be passed to more than one method of a {@code PoolableObjectFactory}
58 * at a time.
59 * <p>
60 * While clients of a {@link KeyedObjectPool} borrow and return instances of
61 * the underlying value type {@code V}, the factory methods act on instances of
62 * {@link PooledObject PooledObject<V>}. These are the object wrappers that
63 * pools use to track and maintain state information about the objects that
64 * they manage.
65 * </p>
66 *
67 * @param <T> Type of element managed in this factory.
68 *
69 * @see ObjectPool
70 *
71 * @since 2.0
72 */
73 public interface PooledObjectFactory<T> {
74
75 /**
76 * Reinitializes an instance to be returned by the pool.
77 *
78 * @param p a {@code PooledObject} wrapping the instance to be activated
79 *
80 * @throws Exception if there is a problem activating {@code obj},
81 * this exception may be swallowed by the pool.
82 *
83 * @see #destroyObject
84 */
85 void activateObject(PooledObject<T> p) throws Exception;
86
87 /**
88 * Destroys an instance no longer needed by the pool, using the default (NORMAL)
89 * DestroyMode.
90 * <p>
91 * It is important for implementations of this method to be aware that there
92 * is no guarantee about what state {@code obj} will be in and the
93 * implementation should be prepared to handle unexpected errors.
94 * </p>
95 * <p>
96 * Also, an implementation must take in to consideration that instances lost
97 * to the garbage collector may never be destroyed.
98 * </p>
99 *
100 * @param p a {@code PooledObject} wrapping the instance to be destroyed
101 *
102 * @throws Exception should be avoided as it may be swallowed by
103 * the pool implementation.
104 *
105 * @see #validateObject
106 * @see ObjectPool#invalidateObject
107 */
108 void destroyObject(PooledObject<T> p) throws Exception;
109
110 /**
111 * Destroys an instance no longer needed by the pool, using the provided
112 * DestroyMode.
113 *
114 * @param p a {@code PooledObject} wrapping the instance to be destroyed
115 * @param destroyMode DestroyMode providing context to the factory
116 *
117 * @throws Exception should be avoided as it may be swallowed by
118 * the pool implementation.
119 *
120 * @see #validateObject
121 * @see ObjectPool#invalidateObject
122 * @see #destroyObject(PooledObject)
123 * @see DestroyMode
124 * @since 2.9.0
125 */
126 default void destroyObject(final PooledObject<T> p, final DestroyMode destroyMode) throws Exception {
127 destroyObject(p);
128 }
129
130 /**
131 * Creates an instance that can be served by the pool and wrap it in a
132 * {@link PooledObject} to be managed by the pool.
133 *
134 * @return a {@code PooledObject} wrapping an instance that can be served by the pool, not null.
135 *
136 * @throws Exception if there is a problem creating a new instance,
137 * this will be propagated to the code requesting an object.
138 */
139 PooledObject<T> makeObject() throws Exception;
140
141 /**
142 * Uninitializes an instance to be returned to the idle object pool.
143 *
144 * @param p a {@code PooledObject} wrapping the instance to be passivated
145 *
146 * @throws Exception if there is a problem passivating {@code obj},
147 * this exception may be swallowed by the pool.
148 *
149 * @see #destroyObject
150 */
151 void passivateObject(PooledObject<T> p) throws Exception;
152
153 /**
154 * Ensures that the instance is safe to be returned by the pool.
155 *
156 * @param p a {@code PooledObject} wrapping the instance to be validated
157 *
158 * @return {@code false} if {@code obj} is not valid and should
159 * be dropped from the pool, {@code true} otherwise.
160 */
161 boolean validateObject(PooledObject<T> p);
162 }